Catalytic processes for the conversion of hydrocarbons are well known and extensively used. Invariably the catalysts used in these processes become deactivated for one or more reasons. Where the accumulation of coke deposits causes the deactivation, reconditioning of the catalyst to remove coke deposits restores the activity of the catalyst. Coke is normally removed from catalyst by contact of the coke containing catalyst at high temperature with an oxygen-containing gas to combust and remove the coke in a regeneration process. These processes can be carried out in-situ or the catalyst may be removed from a vessel in which the hydrocarbon conversion takes place and transported to a separate regeneration zone for coke removal. Arrangements for continuously or semi-continuously removing catalyst particles from a reaction zone and for coke removal in a regeneration zone are well known.
In order to combust coke in a typical regeneration zone, a recycle gas is continuously circulated to the combustion section and a flue gas containing by-products of a coke combustion, oxygen, and water is continually withdrawn. Coke combustion is controlled by recycling a low oxygen concentration gas into contact with the coke-containing catalyst particles. The flue gas/recycle gas is continuously circulated through the catalyst particles. A small stream of makeup gas is added to the recycle gas to replace oxygen consumed in the combustion of coke and a small amount of flue gas is vented off to allow for the addition of the makeup gas. The steady addition of makeup gas and the venting of flue gas establishes a steady state condition that produces a nearly constant concentration of water and oxygen as well as the combustion products in the recycle gas.
In continuous or semi-continuous regeneration processes, coke laden particles are at least periodically added and withdrawn from a bed of catalyst in which the coke is combusted. Regions of intense burning that extend through portions of the catalyst bed develop as the coke is combusted. After this intense burning the catalyst requires reconditioning to restore the noble metal, usually platinum, to its most highly catalytic state and to replace chloride on the catalyst that may be lost in the reaction zone or through the regeneration process. Reconditioning for a reforming catalyst will include contact with a chloride containing compound, to redisperse the platinum metal and replace the chloride that may be lost from the catalyst, followed by a drying step to reduce the moisture content of the catalyst and finally a reducing step to change the platinum metal from various oxidized states to a reduced metallic condition. Alternatively, the reconditioning will involve reversing the order of the redispersion and drying steps, so that the regeneration process and arrangement begins with a combustion zone which is followed by a drying zone to remove moisture from the catalyst particles before they enter the metal redispersion zone. Thus, the prior art processes that use both redispersion and drying steps are divided into two groups--one group that uses drying followed by redispersion and one group that uses redispersion followed by drying. Processes in either group perform these two steps separately and sequentially in two separate zones.
It has now been recognized that two separate steps for drying and redispersion are unnecessary and that regeneration processes that use separate steps are needlessly complex. The present invention is a moving bed catalyst regeneration process with combined drying and redispersion steps. A single reconditioning zone redisperses the noble metal and removes water from the catalyst by countercurrently contacting the catalyst with chlorine and oxygen. The single zone of this invention also promotes rechloriding the catalyst.
The present invention provides a method of reactivating a noble metal catalyst that has been deactivated by the accumulation of coke on its surface, that requires regeneration to remove coke, and that needs redispersion of the noble metal to provide adequate catalytic activity. The present invention is particularly suited for catalysts that use platinum metals and maintain a chloride concentration on the catalyst particles. For such catalyst particles, the arrangement and operation of this method and apparatus will improve the redispersion of platinum on the catalyst particles, improve the drying of the catalyst particles, and allow control of the chloride content on the reconditioned particles. The present invention can also reduce emissions and handling problems associated with gases containing hydrogen chloride. Thus, the present invention can reduce the overall expense of reconditioning such catalyst particles.